Shady practices such as taking cash rebates as kickbacks from media owners and marking up the cost of ad space are pervasive in the $200bn (£137bn) US media buying market, according to a new report that is set to send shockwaves through the global advertising market.

The report – commissioned by the Association of National Advertisers, which represents US marketers controlling about $200bn of annual spend – paints a damning picture.

It identifies practices including agencies purchasing media space on their own behalf and later reselling it to a client after marking up the cost by anywhere between 30% and 90%.

Read the full Guardian article here.